Resonant nanostructures, such as photonic metasurfaces, have created an unprecedented case for enhanced light–matter interactions through local field engineering. However, the presence of resonances fundamentally limits the bandwidth of such interactions. Here, we report on amending the nonlinear optical response of a semiconducting metasurface through Q-boosting, where the Q-factor of a metasurface rapidly increases with time. The coupled-mode theory reveals overcoming the bandwidth limit by coupling a broadband signal to a bandwidth-matched resonance and Q-boosting at a timescale faster than a resonator lifetime. A control–excitation experiment simulation using a tailored Q-boosting silicon-germanium metasurface predicts the third-harmonic enhancement by factors of 8 (peak) and 4.5 (integrated) against the best-case static metasurface. An analysis of free-carrier losses based on experimental data shows robustness to nonradiative losses and offers a viable pathway to increasing the light–matter interactions beyond the bandwidth limit, with implications in nonlinear and quantum optics, sensing, and telecommunication technologies.

中文翻译：

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超出时间带宽限制的 Q 增强超表面的非线性响应

共振纳米结构，例如光子超表面，为通过局部场工程增强光-物质相互作用创造了前所未有的案例。然而，共振的存在从根本上限制了这种相互作用的带宽。在这里，我们报告了通过 Q-boosting 修正半导体超表面的非线性光学响应，其中超表面的 Q 因子随时间迅速增加。耦合模式理论揭示了通过将宽带信号耦合到带宽匹配的谐振并在比谐振器寿命更快的时间尺度上进行 Q 提升来克服带宽限制。使用定制的 Q-boosting 硅锗超表面的控制激励实验模拟预测，针对最佳情况的静态超表面，三次谐波增强因子为 8（峰值）和 4.5（积分）。